75 lines
1.4 KiB
Python
75 lines
1.4 KiB
Python
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# WICHMANN-HILL RANDOM NUMBER GENERATOR
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#
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# Wichmann, B. A. & Hill, I. D. (1982)
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# Algorithm AS 183:
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# An efficient and portable pseudo-random number generator
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# Applied Statistics 31 (1982) 188-190
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#
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# see also:
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# Correction to Algorithm AS 183
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# Applied Statistics 33 (1984) 123
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#
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# McLeod, A. I. (1985)
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# A remark on Algorithm AS 183
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# Applied Statistics 34 (1985),198-200
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#
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#
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# USE:
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# whrandom.random() yields double precision random numbers
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# uniformly distributed between 0 and 1.
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#
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# whrandom.seed() must be called before whrandom.random()
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# to seed the generator
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# Translated by Guido van Rossum from C source provided by
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# Adrian Baddeley.
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# The seed
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#
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_seed = [0, 0, 0]
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# Set the seed
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#
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def seed(x, y, z):
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_seed[:] = [x, y, z]
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# Return the next random number in the range [0.0 .. 1.0)
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#
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def random():
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from math import floor # floor() function
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#
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[x, y, z] = _seed
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x = 171 * (x % 177) - 2 * (x/177)
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y = 172 * (y % 176) - 35 * (y/176)
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z = 170 * (z % 178) - 63 * (z/178)
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#
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if x < 0: x = x + 30269
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if y < 0: y = y + 30307
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if z < 0: z = z + 30323
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#
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_seed[:] = [x, y, z]
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#
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term = float(x)/30269.0 + float(y)/30307.0 + float(z)/30323.0
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rand = term - floor(term)
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#
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if rand >= 1.0: rand = 0.0 # floor() inaccuracy?
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#
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return rand
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# Initialize from the current time
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#
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def init():
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import time
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t = time.time()
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seed(t%256, t/256%256, t/65536%256)
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# Make sure the generator is preset to a nonzero value
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#
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init()
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